I’m still thinking about pivot sprinklers

  

We saw lots of them in Central and West Texas.

(Not my photo.)

 

Water is pumped up the center, goes through the pipe, and comes out the sprinklers.  I get that.  Each section, from the pivot point out, covers an increasingly larger area as it goes around in a circle, so the nozzles on each section need to be sized accordingly; increasingly larger as they get farther from the center source.  I get that too.  The part I have to keep thinking about is the locomotion.  You’ve got maybe ten sections for total length of a quarter mile or so.  The trolleys for each section move in a circle around a pivot point, tracing paths for ten different concentric circles.  Since every circle represents a different distance to complete one lap, I want to know how each trolley happens to do that without messing up the entire apparatus.

 

That quarter mile long pipe of water can’t be so rigid that all one has to do is power the outside trolley and the other ones will follow along.  Each one has to be powered.  The last trolley on the end will have to travel the longest distance, so that one can run constantly.  All the other trolleys have to be geared down just right to run constantly, or they all run the same speed and go intermittently, every one on a slightly different schedule.  Couldn’t count on every trolley running just like it should and never getting bogged down, so the solution has to be that each one runs intermittently.  But how do they know to do that; when to run and when to shut off?  Wires?  Lasers?  What’s the trigger?

 

Wikipedia to the rescue.  There are angle sensors at each joint for each section.  The outer wheels move at a constant slow speed.  When an angle sensor at a joint determines that a section is getting left behind, it triggers the electric motor to drive the wheels on that section until the angle sensor feels like it’s caught up and shuts off the motor.  Each section starts and stops independently, and the whole length of the sprinkler moves in an undulating manner, something like a sidewinder snake, always in nearly a straight line, but never completely straight if you sight along it.

 

Now my mind can be at ease about that.